1. Field of the Invention
The present invention relates to a method of connecting and a structure of connecting an electric wire and a connection terminal for bringing a conductor of an electric wire into press contact to connect with a wire caulking portion of a connection terminal and thereafter welding to connect the conductor and the connection terminal by laser welding.
2. Related Art
Conventionally, as a method of connecting an electric wire and a connection terminal, there is spread a method of electrically connecting an electric wire and a connection terminal by bringing a wire caulking portion mounted to the connection terminal into press contact to connect to caulk on a conductor of the electric wire.
However, in the case of a press contact connection, when the conductor of the electric wire is constituted by a multicore twisted wires structure, although core wires disposed on an outer peripheral side thereof are brought into direct contact with the connection terminal and therefore, conduction is easy to achieve, core wires disposed on a center side thereof is brought into contact with the connection terminal via the core wires on the outer peripheral side.
Further, when dimensions of C/W and C/H of a press contact terminal 1 do not match as shown by FIG. 5, a clearance 5 is liable to be produced between a conductor press contact portion 1a and a conductor 3, which is devoid of reliability of electric connection. Therefore, there poses a problem that many kinds of press contact terminals having dimensions of C/W and C/H matched to respective sizes of electric wires and respective kinds of terminals need to prepare and caulking operation needs to control to thereby increase fabrication cost.
Hence, in order to prevent contact resistance at a press contact portion from being dispersed, as shown by FIG. 6, there has been proposed a connecting method of bringing the conductor 3 of an electric wire 2 into press contact to connect with the conductor press contact portion 1a of the connection terminal 1 and thereafter irradiating laser beam 9 from a laser generating apparatus 8 to the conductor 3 exposed at the center portion and the front and rear portions of an upper face of the conductor press contact portion 1a to thereby weld the conductor press contact portion 1a and the conductor 3 (for example, refer to JP-A-2-103876).
However, according to the above-described connecting method, as shown by FIG. 7, there poses a problem that a terminal material melted by irradiating the laser beam 9 is absorbed by clearances of the conductor 3 and a large recess 13 is produced at a laser welded portion 11 to thereby reduce welding strength or the like. Further, in laser welding, the welding is carried out by irradiating the laser beam having high density energy and therefore, rapid heating or rapid boiling of the terminal material and the conductor is brought about which may bring about explosive scattering (splash phenomenon).
Hence, there has been proposed a laser welding terminal in which a wire caulking portion of a connection terminal is provided with a projected portion or a thick-walled portion for replenishing a melted volume and a recess produced by irradiating laser beam is filled by the melted projected portion or the melted thick-walled portion (for example, refer to JP-A-6-302341).
Further, as shown by FIG. 8, there has been proposed a structure of a connecting portion in which there is formed an irradiation port 17 for irradiating laser beam at a pair of core line press contact pieces 16, 16 formed at a press contact portion 15 of a connection terminal 14 and respective strands of the core line portion 3 are subjected to laser welding by irradiating laser directly to the core line portion 3 at inside of the press contact portion 15 by passing the irradiation port 17 (for example, refer to JP-A-2000-231944).
According thereto, even when the connection terminal is brought into press contact therewith without previously operating excessive press contact force to a portion of core lines which are not welded, respective strands can be welded together at inside of the press contact portion, and electric resistance between the connection terminal and the electric wire can be restrained to reduce by restraining to reduce contact resistance among the respective strands.
However, when the electric wire and the connection terminal are connected by laser welding described in JP-A-6-302341 and JP-A-2000-231944, mentioned above, and the like, as described above, the projected portion or the thick-walled portion for replenishing the welded volume needs to provide at the wire caulking portion of the connection terminal, or the irradiation port for irradiating laser beam needs to form at inside of the press contact portion of the connection terminal to thereby pose a problem of increasing working steps in fabricating the connection terminal or increasing cost of the connection terminal owing to complicated formation of a die for pressing a connection terminal.
Further, in recent times, there are a number of cases in which materials (physical properties) of a connection terminal and an electric wire differ from each other. For example, although Cu alloys are frequently used for the material of the connection terminal, in contrast thereto, a material which is difficult to achieve electric conduction of aluminum series or Fe—Ni series or the like is frequently used for the material of the electric wire. Whereas a melting point and heat of melting of aluminum are 660° C. and 94.5 cal/g, and a melting point and heat of melting of copper are 1083° C. and 50.6 cal/g and physical properties thereof differ from each other significantly and therefore, it is difficult to ensure excellent connection function by applying laser welding, mentioned above.